Flora of North America species comparison

Potentilla norvegica is considered native in both North America and Eurasia, with the American race occasionally recognized as subsp. hirsuta for the stiff hairs on the stems, petioles, and pedicels of most plants in the flora area. This feature and other purported differences between the two races, in addition to being relatively subtle and inconstant, can be found in both America and Eurasia, though undoubtedly at least in part as introductions. Some populations in eastern Canada with glabrous stems have been distinguished as var. labradorica (for example, M. L. Fernald 1950), but such plants typically are intermixed with hairy individuals. The Löves (Á Löve 1954; Á Löve and D. Löve 1966) have argued that all three variants should be treated as distinct species due to chromosomal differences (hirsuta 2n = 56; labradorica 2n = 42; norvegica in the narrow sense 2n = 70) and obligate apomixis. Further research is needed to determine the taxonomic validity and rank of these expressions. If treated as species, P. flexuosa antedates P. labradorica (as noted by J. Soják 1969), while P. monspeliensis, although commonly used for the American race, is based on a European type (as summarized by A. Kurtto et al. in J. Jalas et al. 1972+, vol. 13).

An even greater challenge is determining native versus introduced ranges, especially given the likelihood that both native and Eurasian populations are widespread in North America. Achenes are produced prolifically and easily dispersed, to the extent that Potentilla norvegica is a contaminant in clover and hay fields and considered a weed at least in Canada (P. A. Werner and J. D. Soule 1976).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Subspecies 3 (2 in the flora).

Southern arctic and subarctic plants differ from the northern arctic ones in presumably independent features. Where the two forms are sympatric (western Greenland, northern Quebec, Baffin Island), they appear to remain distinct even in mixed populations and are accordingly treated as subspecies.

Although some features of scattered plants in Alaska and Yukon approach subsp. nivicola Jurtzev & V. V. Petrovsky (described from northeastern Asia), such plants do not otherwise correspond fully with this taxon. Possible hybrids between Potentilla hyparctica and P. pulchella (sect. Pensylvanicae) are addressed in the discussion of sect. Pensylvanicae. Presumed hybrids with P. villosa from the Aleutian Islands, characterized by the combination of basally thickened styles and lack of cottony hairs on leaflet abaxial surfaces, have been named P. ×aleutica Soják.

(Discussion copyrighted by Flora of North America; reprinted with permission.)